\chapter{Background}\label{ch:background}

Spacecraft formation flying is a concept that employs two or more spacecraft in a tightly-controlled spatial configuration, which can yield improved performance for a variety of mission objectives. Use of the relative GPS positioning technique can potentially achieve centimetre-level accuracy in formation flying missions, even in real time. The space projects currently undertaken at ASCER/UNSW have led to development of spaceborne GPS receiver upon the Namuru receiver developed by Surveying and Spatial Information System (SSIS) at UNSW. 

\section{Previous work}

Currently the Narumu receiver’s architectures and relative navigation algorithms for the space missions are tested only by mathematical simulation and the hardware GPS signal simulator. The Formation flying strategy is not yet confirmed to work well as expected in a real GPS signal environment. The idea of this proposal is to use the UAVs to have an affordable solution for testing the Namuru’s formation flying performance in real GPS signal environments. 
This project aim to deliver a robust quadrotor based UAV platform with NAVCON – a small embedded navigation/control PCB board newly developed by SSIS. It fuses the GPS and the MEMS inertial sensors on the DSP core to provide practical solutions to control and stablise the UAV. The NAVCON can be employed directly when developing the UAV formation flying technology with this project. By having UAVs as test platform, the cost will be minimised in comparison to failed in action on Cubesat. 
This project is cooperation with UNSW Canberra and the School of Mechanical and Manufacturing Engineering at UNSW, directed by SSIS. The outcomes of this project will provide for not only testing the space relative navigation receivers, but also will potentially allow strapdown of a space mission payload to the UAV counterpart, which can complement the space missions by: (1) rapid deployment for specified/emergency services; (2) real-time response to emergency services; and (3) more flexibility to local area services, when the space system is not available.

